Light-responsive self-strained organic semiconductor for large flexible OFET sensing array

With the wide application of organic semiconductors (OSCs), researchers are now grappling with a new challenge: design and synthesize OSCs materials with specific functions to satisfy the requirements of high-performance semiconductor devices. Strain engineering is an effective method to improve the semiconductor material’s carrier mobility, which is fundamentally originated from the rearrangement of the atomic packing model of materials under mechanic stress. Here, we design and synthesize a new OSC material named AZO-BTBT-8 based on high-mobility benzo[b]benzo[4,5]thieno[2,3-d]thiophene (BTBT) as the semiconductor backbone. Octane is employed to increase molecular flexibility and solubility, and azobenzene at the other end of the BTBT backbone provides photoisomerization properties and structural balance. Notably, the AZO-BTBT-8 photoisomerization leads to lattice strain in thin-film devices, where exceptional device performance enhancement is realized. On this basis, a large-scale flexible organic field-effect transistor (OFET) device array is fabricated and realizes high-resolution UV imaging with reversible light response.


Supplementary Methods
Molecular synthesis. All reagents and chemicals were obtained from commercial sources and used without further purification unless otherwise noted. All reactions were performed under an inert atmosphere of argon in dry solvents using standard Schlenk techniques. 1 H and 13 C spectra were recorded on Bruker-400 MHz NMR ARX400. Chemical shifts of 1 H and 13 C NMR signals were quoted to tetramethylsilane (δ = 0.00 ppm) and CDCl3 (δ = 77.00 ppm) as internal standards, respectively. Mass spectra were recorded on a Bruker APEX IV mass spectrometer. The synthetic route used to obtain linker AZO-BTBT-8 is outlined in Scheme S1. Compound 1-7 were synthesized according to the literatures. 1 (15 mg, 0.013 mmol) were added in a specially designed conical flask protected with nitrogen. 30 mL degassed solution (VTHF: Vwater = 5:1) was added after the apparatus was sealed. The system was held at 80 ℃ and carefully stirring for 24 h. 1  UV-Vis absorption. UV-Vis absorption measurements of solution (acetonitrile as solvent) and thin films (on quartz substrates) were determined with a Perkin-Elmer Lambda 950 UV/Vis spectrometer. The thin films were directly prepared by spin-coating (3k rpm, 120 s).

The optical microscopy (OM) and the polarized optical microscopy (POM) with
heat stage were obtained on silicon substrates by using Nikon Eclipse LV100 POL, Japan in reflection mode on a home-made heat stage.

Calculation method for the percent conversion of AZO-BTBT-8 molecules:
The fitting and calculation can be determined from UV-Vis spectra, current plots and fitting curves from in-situ conductive AFM.
Photochromism is defined as a reversible change in a chemical species between two forms.
To calculate the percent conversion (xe) from AZO-BTBT-8-trans (A) to AZO-BTBT-8-cis (B), a semiempirical approach is used, assuming that a pseudo-first-order process with linear intensity dependence adequately describes the present photochromic system.
The overall change in concentration of AZO-BTBT-8-cis (B) with time can be simply given by the following rate equation: Integration of the rate equation yields: where A and B are the concentrations of AZO-BTBT-8-trans and AZO-BTBT-8-cis, kUV is the photochemical rate constant, A0 is the total concentration of all the AZO-BTBT-8 molecules. In this case the absorbance maximum was used as analyzing wavelength of plot peaks accordingly in Supplementary Fig. 9a.
Where a, b are fitting constants. At the photostationary state, the percent conversion The bending method and stain estimation: To evaluate the bending stability of the OFETs, the PET substrate was bent from flat to curved along an axis running exactly through the transistors by a home-made setup ( Supplementary Fig. 19). The strain S induced in a particular layer having a thickness L located on the surface of a substrate having a thickness S by bending the substrate into a radius R is given by the following equation: where = / , is the thickness of the layer, is the thickness of the substrate; andχ = / , is the Young's modulus of the layer, is the Young's modulus of the substrate. 3 Simply S can be expressed as: Where D is the thickness of the substrate, R is the radius of curvature. Meanwhile, L is also related to strain which can be directly read from the screw micrometer.

Supplementary tables and figures
Supplementary